Offshore structure



Nov. 20, 1962 R. P. KNAP 3,064,437

OFFSHORE STRUCTURE Original Filed Dec. 20, 1955V 8 Sheets-Sheet 1 INVENTOR. Richard P. Knapp,

Nov. 20, 1962 R. P. KNAPP 3,064,437

OFFSHORE STRUCTURE original Filed Dec. zo, 1955 v s sheets-sheet 2 w Q cu F IG. 8

FIG. 7.

F IG. 6.

FIG. 5.

INVENTOR. Richard P. Knapp,

ATTORNEY.

Nov. 20, 1962 R. P. KNAPP 3,064,437

OFFSHORE STRUCTURE Original Filed Dec. 20, 1955 8 Sheets-Sheet 5 Fie. I3. l'

I FIG. l'

INVENToR. Richard P. Knapp, BY

ATTORNEY.

INVENT hard P. Kna

O ATTOR 8 Sheets-Sheet 4 Ric R. P. KNAPP OFFSHORE STRUCTURE Original Filed DSG. 20, 1955 Nov. 20, 1962 Nov. 20, 1962 R. P. KNAPP OFFSHORE STRUCTURE Original Filed Dec. 20, 1955 Ila |2a g l i l Il i l I 24 25:.' asf 25j 25 8 Sheets-Sheet 5 lllllllflll flllml-lllllllm INVENTOR. Richard P. Knapp,

Nov. 20; 1962 R. P. KNAPP 3,064,437

` OFFSHORE STRUCTURE original Filed Dec. '20) 1955 s sheets-Sheet SEA COC CONTROL INVENTOR. Rchad P.I K nupp,

Nov. 20, 1962 R. P. KNAPP 3,064,437

OFFSHORE STRUCTURE Original Filed Dec. 20, 1955 8 Sheets-Sheet 7 Denman 22 BETA ABLE Pon ons `SEA LEVEL il )MAW 24 *INI/ENTOR. RcharddP. Knapp,

ATTORNEY.

NovQZO, 1962 R. P. KNAPP OFFSHORE STRUCTURE 8 Sheets-Sheet 8 Original Filed Dec. 20, 1955 DERRIGK FIG. 35.

'VINI/ENTOR. Rchardf. P. Knapp,

SEA LEVEL ocEAN noon ATTORN Y.

United States Patent Oilce 3,064,431 Patented Nov. 20, 1962 3,064,437 OFFSHORE STRUCTURE Richard P. Knapp, Houston, Tex., assigner, by mesne assignments, to Jersey Production Research Company, Tulsa, Gkla., a corporation oi Delaware Original application Dec. 20, 1955, Ser. No. 554,375, now Patent No. 2,938,354, dated May 31, 1969. Divided and this application July i6, 1959, Ser. No. 327,519 6 Claims. (Cl. 61--46.5)

The present invention is directed to a structure suitable for use in oifshore operations. More particularly, the invention is directed to a portable, stable structure which is easily transportable to a marine location. In its more specific aspects, the invention is directed to miarine structure which has stability and which is easily transportable to an offshore location.

This application is a division of U.S. Serial No. 554,375 tiled December 20, 1955, now Patent No. 2,938,354 for Richard P. Knapp and entitled Method and Structure for Offshore Operations.

The present invention .may be briefly described as a portable, stable structure suitable for use in offshore marine operations which comprises a bottom bearing member having a plurality of interconnected vertically extending buoyancy colummns connected to the bottom bearing member on their lower ends. A platform is supported by the buoyancy columns on the upper ends of the buoyancy columns, so that the columns are peripherally inwardly spaced a certain distance; that is, there is a certain overhang of the platform with respect to the column. Vertically adjustable auxiliary buoyancy means are arranged on all or a selected of the buoyancy columns with a portion of the buoyancy means extending inboard of the structure and the remaining portion of the buoyancy means extending outboard of the structure. The bottom bearing may be provided simply Ias a mat but may be constructed such that it has buoyancy and may be suitably compartmented and provided with sea chests, valves, and the like `for flooding the compartments of the bottom bearing member with water to ballast same and with suitable air connections to blow the water from the compartments. Suitably the buoyant bottom bearing member may have an open bottom and buoyancy given thereto by maintaining a selected air pressure therein.

The structure of the present invention is provided with vertically adjustable spuds arranged in the buoyant columns, such that they may be extended through the lower end of the buoyant columns to serve as mooring and anchoring means by positioning the spuds into the underlying bottom of the marine location where the structure may be located. The spuds are vertically adjustable such that they may be extended or retracted into the buoyant columns. The spuds may be extended or retracted by employing jacks of the hydraulic type and the like, suitable screw and wedge mechanisms, hydraulic means and the like for raising and lowering the'spuds. The spuds may suitably be provided with a hydraulic lock, clamps or pins or other means for locking the spuds in position as may be desired.

The present invention is also directed to a method for preloading the soil on which the device of the present invention is positioned. Briefly, in practicing the method of the present invention, the structure is floated into position with the bottom bearing member off bottom. The vertically adjustable auxiliary buoyancy means are then flooded a suiiicient amount to cause the bottom bearing member to sink to the bottom. The device is then rmly positioned against vertical movement by driving the spuds downwardly into the soil underneath the bottom bearing member. This is suitably done by exerting hydraulic pressure against the spuds although other means may ing moisture from the compacted soil.

be employed. Thereafter, the hydraulic pressure is released `from the spuds, which have now been driven into the soil and which allows the structure to have some vertical movement but prevents any lateral movement due to Iwave action, and the like.

The auxiliary buoyancy means are then dewatered which allows the buoyancy means or tanks to rise on the buoyant coliunns such that they may be rmly attached lto the columns by suitable attaching means. The force of the tanks vertically is then exerted on the columns. The auxiliary buoyancy tanks are then flooded with water to the extent that the water level in the auxiliary buoyancy means or tanks is greater than sea level. This is accomplished yby pumping water into the auxiliary buoyancy means rather than relying solely'on the water entering same through the sea chest. By flooding the auxiliary buoyancy means, the auxiliary buoyancy means moves downwardly causing the buoyant columns to move downwardly therewith since the auxiliary buoyancy means are connected thereto. By adjusting the level of the water in the auxiliary buoyancy tanks, the columns and bottom bearing member are provided with a maximum preload in excess of the preloading which will be maintained on the structure during the marine operations.

For example, the preloading on the columns and bottom bearing 4member may be in the range from about 500 to about 2000 pounds per square foot. This preloading depends on the operating load on the bottom. In the Gulf Coast area a preload of 500 to 2000 pounds per square inch will usually suiiice. Ordinarily preloads in the range from about 500 to 1000 pounds per square inch will be satisfactory. `Of course, it is realized that the preloading in the practice of the present invention will depend on the operating load on the sea bottom and may vary depending on the lregion where the oishore opera-J tions are conducted.

As the auxiliary buoyancy means or tanks sink, the weight thereof bears down on the buoyant -columns and causes the soil under the mat to be compacted by squeez- The auxiliary ibuoyancy tanks may be adjusted with varying amounts of `water or preload the level the structure where the structure is not on an even keel.

In practicing the present invention, the auxiliary buoy-v ancy `means or tanks are left on bottom, locked tothe buoyant columns for a suiiicient length of time to compact the soil under the bottom bearing means. This time may suitably range from about 4 hours to'about 48 hours. Times from about 4 hours to about 24 hours `may be satisfactory and preferred.

The spuds are then locked into position against vertical movement by suitable locking means which may be hydraulic pressure exerted against the spuds to prevent vertical movement. The auxiliary buoyancy means or tanksl are then dewatered to a floating position, unlatched, and emoved from the buoyant columns. ln practicing the method of the present invention, a more stable structure is possible than heretofore.

It is understood that the'strueture of the present invention may comprise a plurality of extension supporting members constituting building yblocks made up 0f interconnected, vertically extending columns. Thus, the platform may be supported on a plurality of building blocks or extension supporting members connected to the bottom bearing members and when it is desirable to extend or lower the height of the structure for use in deeper or shallower water the platform may be removed and building blocks or extension supporting mem-bers either added to the structure of subtracted therefrom. The ext-ension supporting members comprising the interconnected, vertically extending columns would be connected to each other, either by welding or by a bolted ange arrangement which lwould allow easy removal of the extension supporting members from or addition of the extension supporting to 'the structure.

It is contemplated that the auxiliary buoyancy means arranged on all or a selected of the buoyant columns may be removable therefrom. In short, the auxiliary buoyancy means may be provided with a slot and latch arrangement for placing same on the buoyant columns or the buoyancy means may be provided with a removable segment for arranging same on the columns. Alternatively, the auxiliary buoyancy means may comprise a plurality of buoyant chambers interconnected and arranged around selected or all of the buoyant columns. The buoyancy means may also comprise a plurality of buoyant chambers arranged one upon another and separable from each other such that buoyant chambers may be added to provide additional buoyancy or buoyant chambers may be subtracted as may be desired.

Where the buoyancy means are provided with a removable segment, it is contemplated that the buoyancy means and the segment may be provided with opposing surfaces defining complement-ary obtuse and acute angles with the horizontal axis of the buoyancy means, the sum of the angles being approximately 180. In short, the buoyancy means may have a surface defining an obtuse angle and the segment may have a surface defining an acute angle or vice versa, the sum of the angles being approximately 180.

' It is contemplated that the auxiliary buoyancy means may be inatable such that when it is desired to provide auxiliary buoyancy the auxiliary buoyancy means would be inflated and when the auxiliary buoyancy is no longer required the buoyancy means may be dellated as desired.

. Thus, the present invention relates to a portable marine platform which provides a stable foundation for machinery, drilling equipment, storage tanks, and the like, a base for salvage operation located over a body of water. The platform involving the structure may be moved with or without the drilling equipment and the like from one water location to another as desired or it may be converted to an improved type of permanent marine structure. The platform is easily adjusted to permit safe use in a wide range of water depths.

Ihe invention is particularly suitable to well drilling operations such as oil and/or gas or sulfur wells and may be used with an auxiliary vessel or platform or suitably may be self-contained to provide the necessary living quarters and warehouse facilities to conduct such marine operations.

The present invention will be further illustrated by reference to the drawing in which:

FIG. 1 is a side elevation of the platform structure.; FIG. 2 is a horizontal section along line 2-2 of FIG. 1;

FIG. 3 is a vertical section along line 3-3 of FIG. 1;

FIG. 4 is a vertical section along line 4-4 of FIG. 1;

FIG. 5 is a side elevation 0f the platform structure in a normal well drilling position;

FIG. 6 is a side elevation, showing buoyancy transport units attached and the platform ready for movement to a new drilling site;

FIG. 7 is a side elevation, showing buoyancy transport units attached and the platform in a normal moving position;

FIGS. 8 and 9 are `side elevations, showing larger or multiple buoyancy transport units attached and the platform structure in a normal moving position;

FIG. 10 is a side elevation of the platform structure in lan alternate drilling position with buoyancy transport units attached and submerged;

FIG. 11 is a side elevation of the platform structure shown in FIG. 10 after moving to deeper water and the addition of one truss bay or extension member;

FIGS. 12 and 13 are side elevations of the platform structure shown in FIG. 10 after moving to deeper Water and the addition of two and three truss bays or extension members;

FIG. 14 is a side elevation of the platform in a drilling position with buoyancy transport units attached;

FIG. l5 is a plan view of the platform shown in FIG. 14, showing the working deck area and one arrangement of the buoyancy transport units;

FIG. 16 is a vertical section through the platform along line 16-16 of FIG. 115

FIG. 17 is a horizontal section through the platform along line 17-17 of FIG. 14;

FIG. 18 is a side elevation of the platform in a drilling position with the buoyancy transport units removed;

FIG. 19 is a fragmentary view showing a buoyancy transport unit composed of several individual, vertical, buoy-ant vessel compartments;

FIG. 20 is a section-al top view of FIG. 19;

FIG. 21 is a horizontal section similar to FIG. 20 showing the use of a slotted barge or chamber for a buoyancy transport unit;

FIG. 22 is a vertical section through an inflatable buoyancy transport unit and a transport column;

FIGS. 23, 24, and 25 are top and side elevations of another type of removable buoyancy transport unit;

FIG. 26 is a side elevation of the platform in a permanent position with buoyancy transport units and transport columns removed;

FIG. 27 is a plan view of the platform shown in FIG. 26;

FIG. 28 is a side elevation of the platform with the buoyancy means in transporting position;

FIG. 29 is a sectional view taken along the line 29-29 of FIG. 28;

FIG. 30 is an enlarged plan view of one of the buoyancy means of FIGS. 28 and 29;

FIG. 31 is a View partly in section taken along the line 31-31 of FIG. 30;

FIGS. 32 and 33 are top and side views, respectively, of another type of buoyancy transport means;

FIG. 34 is a perspective view of the platform, equipped -with drilling derrick, being transported;

FIG. 35 is a perspective view of the plateform of FIG. 34 in a drilling position and with the buoyancy means removed.

Referring now to the drawings in which identical numerals will -be employed to designate identical parts, and

particularly to FIGS. 1 to 4, the structure comprises a structure generally indicated by the numeral 11 which is of rectangular form and having a generally flat working surface generally designated by the numeral 12. The working surface or platform 12 is suitably supported by longitudinal or transverse structural members 1-3 which are supported by a trusswork indicated generally by the ntnneral 14 composed of vertically extending columns 15, diagonal members 16, and horizontal girt members 17. rPhe structure is also provided with buoyant columns 1S. The trusswork 14 and the buoyant columns 18 terminate in a bottom bearing member 19 which is of general rectangular form with a suitable opening or openings 2G for the conducting of drilling operations and the like. The bottom bearing member is suitably constructed of longitudinal and transverse structural members and may be provided with suitable compartments, chambers, and the like 21.

Extending through the columns 18 are bottom penetrating mooring spuds indicated Vgenerally by the numeral 10 which penetrate into the soil below the bottom bearing member 19 to provide resistance to lateral movement, overturn, and vertical sinkage of the structure. The spuds 10 are adjustable vertically and may be extended or retracted as may be desired.

While the platform structure 1,1 is shown to have a square working deck and a square bottom bearing member with four buoyant columns forming the four corners of a square horizontal section, it is possible to have other configurations but it is preferred to have a square structure because it provides the most stable structure for a given structural Weight. It is to be understood, however, that other shapes and configurations may be used and may be preferable where structural Weight is a secondary consideration. For example, a rectangular plan with the length greater than the width may be more desirable where the width is limited by existing land facilities and a greater length is necessary to obtain the required Working deck or bearing bottom member area.

As pointed out supra, it is not necessary that the bottom bearing member 19 be a watertight structure and it is preferable that the bottom bearing member 19 have as little buoyancy as possible when the structure is in the moving position. For maximum stability during moving operations the bottom bearing member should be completely ooded or open to the sea, with buoyancy limited to the volume of water displaced by the structural members. As pointed out before some Water-tight compartmentation may be desirable for the storage of liquids or to float the platform on the surface of the sea for delivery, overhaul and/ or repairs.

Referring now to FIG. 5, the structure is shown in a normal drilling position with a drilling rig 22 mounted on the platform 12. The spuds have been extended and have been driven into the underlying land 23 with the platform 12 being located a suitable distance above the water level 24 for safe operations. The structure of FIG. 5 may be converted from a stable, temporary, and portable drilling platform to a permanent platform as shown in FIGS. 26 and 27 by driving bearing piles, such as 25, through the vertical columns and/ or through the buoyant column 18. The number of bearing piles, the depth of penetration, and the size may be determined by the soil and oceanographic conditions encountered at the site of the permanent installation.

It is to be noted that FIGS. 26 and 27 are modified structures 11a having a platform 12a. As shown by the plan view in FIG. 27, the platforrn 12a of the structure 11a has a cross shape which provides a maximum area for this particular shape.

Referring now to FIGS. 6 to 9, auxiliary buoyancy means generally indicated by the numeral 26 are attached to the buoyant columns 18 such that the auxiliary buoyancy means 26 are vertically adjustable therein and extend inboard and outboard of the structure. By providing the auxiliary buoyancy means to extend both inboard and outboard, greater stability of the structure is provided than would be otherwise if the auxiliary buoyancy means were completely inboard or completely outboard of the struct-ure. The dotted lines in FIG. 6 show the auxiliary buoyancy means 26 to be vertically adjustable and the position assumed in moving the structure from the underlying land bottom 23. It is to be noted in FIG. 6 that the vertically adjustable spuds 10 have been retracted into the interior of the columns 18 and the structure 11 is in position to be moved offshore. As the auxiliary buoyancy means 25 are dewatered, or inflated if a collapsible type of buoyancy means is used, and with buoyancy provided on the columns 18, sufiicient buoyancy is given to the structure 11 to float same off the sea bottom 23. It is to be noted that the auxiliary buoyancy means 26 assume the position as sho-Wn in FIG. 7 at sea level to provide a floating structure.

As illustrated in FIGS, 8 and 9, additional numbers of auxiliary buoyancy means 26 may be added to the structure as desired to oat the structure 11 higher in the water or to give a greater freeboard as shown. The plurality of auxiliary buoyancy means may be suitably locked one to the other by suitable locking means and are separable one from the other and are superimposed on each other by arranging same either below or above the original buoyancy means as provided in FIGS. 6rl and 7. Of course, it is realized and understood that buoyancy means 6 may be removed as desired to reduce the freeboard. After the structure has been raised to a moving position, as shown in FIGS. 7, 8 and 9, it may then be towed or moved to the next desired location and then again sunk to the underlying land bottom 23 and anchored thereto by reversing the steps of the operation as has been described. p

As illustrated in FIGS. l0 through 13, inclusive, the structure 11 is adjustable in height and is suitably constructed of extension supporting members or building block sections which are generally designated by the numeral 30. In FIG. l() the structure 11 with the drilling rig 22 is shown landed on bottom 23 with the spuds 10 sunk in the earth and with the bottom bearing member 19 resting on the'bottom 23. Auxiliary buoyancy means 26 are resting on the bottom 23, having been lled With water. Assuming that it is desired to raise the level of the platform 12 above the Water level 24 preparatory to a move into deeper Water, the drilling rig 22 and platform 12 would be removed Vand another building block 30 would be brought into position and placed on the uppermost of the building blocks 3i). The building blocks 30 would be suitably connected to those already in place, such as by Welding or by bolted flanges and then the platform 12 and drilling rig 22 would be replaced on the structure, as shown in FIG. 11. Thereafter, as illustrated in FIGS, 6 to 9, the structure would be moved from water having a depth of about 33 feet, as shown in FIG. 10, with the platform 12 about 35 feet above water to water having a depth of about 50 feet with platform 12 being about 40 feet above the Water level 24, as shown in FIG. 1l. The spuds 16 would again be lowered and the structure could then be used again for drilling operations and the like.

yIn FIGS. 12 and 13 illustrations are given for identical building blocks 30 to provide a structure with respect to FIG. 12 usable in water of about 73 feet depth providing a platform about 24 feet above water level. In FIG. 13, the structure is illustrated which is suitable for drilling operation in foot water.

Referring now to FIGS. 14 through 16 it is to be noted that the auxiliary -buoyancy means 26 are of general cylindrical shape and extend both inboard and outboard of the structure 11. The spuds 10 are shown driven into the underlying land bottom 23 and with the auxiliary buoyancy means 26 resting on bottom. `In FIGS. 14 through 16 the auxiliary buoyancy means 26 are a1'- ranged permanently on the structure 11 surrounding the columns 18 and 15. Buoyancy means 26 are shown arranged on the columns -18 which the spuds 10` removed. FIG. 17 is a plan view showing the opening 20 of the structure 11. When the auxiliary buoyancy means 26 are employed, it will be necessary to provide means for introducing water into and removing Water from the auxiliary buoyancy means 26. To this end a flexible connection such as 31 provided with a valve 32 may be arranged to extend from the platform 12 to the buoyancy means 26. This flexible connection 31 may be a suitable hose which may be of deformable material and reinforced with metallic members or may be a braided metal hose band the like. The flexible member 31 may extend inboard and outboard of the structure to provide air pressure to the members 26 or to relieve air pressure therefrom. It is also likely that water may also be pumped into the buoyancy means 26 through line 31 or sea cocks may be provided in each of the buoyancy means 26 and controlled by a valve rod extending up to platform 12.

FIG. 18 is a view similar to FIG. 16 but shows the buoyancy means 26 removed therefrom and the spuds 10 driven into the land bottom 23.

In FIGS. 19' and 20, a modified auxiliary buoyancy means 26b comprised of a plurality of interconnected vessels 26c are shown. The interconnected vessels 26C are suitably connected by structural members 33 and arranged around selected or all of the columns 18 as may 7 be desired. It will be apparent from FIGS. 19 and 20 that the vessels 26C may easily be removed from around any or all of the columns 181as may be desired.

In FIG. 21 a different type of removable auxiliary buoyancy means is illustrated in which a barge or vessel, such as 34, provided with a slot 35 is arranged around the columns 18 and locked thereon by means of a locking mechanism, such as pin 36. It is to be noted that the vessel 34 may be easily removed by removing the locking mechanism 36 and guiding the vessel 34 o the column 18. *It is to be noted that the vessel 34 extends both inboard and outboard of the structure. A Another type of auxiliary buoyancy means is shown in FIG. 22 in which an inilatable member 37 is arranged on the columns 18 to surround same. The inliatable member 37 extends bothinboard and outboard of the structure and may suitably be deflated and left to rest on the bottom bearing member 19 when not in use and inated when in use. To this end, a suitable exble connecting member, such as 31, extending to the platform '12 and provided with a valve 32 may be used for inflation and deflation as desired.

Referring to FIGS. 23, 24, and 25 another type of removable auxiliary buoyancy means is provided. Auxiliary buoyancy means 38 is provided with a removable pie-shaped segment 39 which may suitably be removed from the columns 18 to allow oating oif of the auxiliary buoyancy means 38 therefrom. The auxiliary buoyancy means 38 and the pie-shaped segment 39 thereof are provided with complementary sloping surfaces 40 and 41 which define complementary acute and obtuse angles with the horizontal axis of the member 38. By virtue of providing sloping surfaces 40 and 41 the segment 39 may suitably be pinned and latched to the auxiliary buoyancy means 38. Passageways 42 are provided to receive pins, not shown, to latch the auxiliary buoyancy means 38 and segments 39 thereto.

Referring specifically to FIGS, 29 and 30, the buoyancy transport means 51 are composed of two equal or approximately equal tank sections 52 which are joined at one side by a hinged connection '3. The two sections 52 provide an annular central opening 54 large enough to accommodate the buoyancy columns 18. The sections 52 are opened and closed by hydraulic means generally indicated by numeral 5S which may comprise a piston and cylinder arrangement operated by a suitable pump. The sections 52 may be locked together in a closed position by a pin such as 56. The buoyancy transport means 51 may also be of the type shown in FIGS. 23, 24, and 25. Each of the sections 52 of the buoyancy transport means is provided with a sea cock controlled by a valve wheel 57. The sections are also provided with a deep well type pump 58 provided with a conduit 59 projecting into the tank section for the purpose of dewatering the sections when desired. The water in the sections may be pumped out by means of the pump 58, or the water may be forced out by pumping in air and opening the sea cocks by valve wheel 57. The tank sections 52 are provided with vents A60 for the release of air when flooding the sections with water.

As shown in FIGS. 30 and 31, the buoyancy means 51 are provided with latching means 61 for the purpose of latching Vthe buoyancy means to the columns 18. This latching means is each comprised of two upright racks 62 having adjustably mounted thereon a cross bar 63 for vertical and horizontal movement. The cross bar 63 is provided on one end thereof with a U-shaped clevis 64 which engages with one of a series of vertically spaced apart annular shoulders 50 of the columns 18. Engagement of these latching means and dewatering or ooding of the buoyancy means affords a lifting or lowering force to be exerted on the platform structure 11.

The device as shown in FlGS. 28 through 31 operates and may be used in a similar fashion to the other embodiments shown.

the columns 18. After the auxiliary buoyancy means.

70 have been placed in position, they may be suitably locked therein by suitable locking means indicated generally by the numeral 72. This locking mechanism may suitably be a member which will make a snug t around the column 18 to prevent lateral lmovement and to allow vertical movement as may be desired. For example, a horizontally retractable member which has an outer arcuate surface, such as indicated, may be positioned in contact with the outer periphery of the columns 18 to lock the auxiliary buoyancy means 70 against lateral movement but for vertical movement thereon as desired. It is understood that the means 70 may be locked against vertical movement as well.

In practicing the present invention with reference particularly to FIGS. 14 and 15, the structure 11 would be floated into position and the auxiliary buoyancy means 26 would then be flooded a suiiicient amount of water to cause the structure to sink to the sea bottom 23 with the mat 19 on bottom. Thereafter, the spuds 10 would be sunk or forced intodthe earth 23 by suitable hydraulic means, not shown. Hydraulic pressure is then released which will allow some vertical movement of the structure 11. The auxiliary buoyancy tanks 26 are then dewatered which allow them to rise on the columns 18 to a floating position. The auxiliary buoyancy means 26 are then latched or locked to the columns 18 such that any force exerted by the tanks 26 will be exerted on the columns 18. The auxiliary buoyancy tanks 2-6 are then ilooded with water or has water pumped in to a level above the sea level sufficient to provide a maximum preload on the bottom bearing member 19 in excess of that which will be employed on the structure 11. As the auxiliary tanks 26 sink to the bottom 23, the soil making up the bottom 23 is compacted under the bottom bear- Ving member 19 to cause moisture to be squeezed out therefrom. The tanks 26 are left on bottom to provide the maximum preload for the time indicated and then the spuds 10 are locked into position against vertical movement. The tanks 26 are then dewatered to a oating position, unlatched from the columns 18 and then removed therefrom as desired.

FIGS. 34 and 35 are perspective views illustrating the structure 11 which could be any of the embodiments as described in the transporting position with the buoyancy means attached and in the anchored position with the buoyancy means removed.

The present invention is of considerable utility and advantage in that a stable marine structure is provided which is easily removable and may be anchored permanently at a desired marine location. The structure has stability in that the auxiliary buoyancy means extend both inboard and outboard of the structure. Furthermore, the structure is adjustable in height and may be moved from shallow to deep water or vice versa and used therein. Furthermore, the structure is of considerable utility in that the auxiliary buoyancy means may be rranged permanently on the structure or releasable thererom.

The nature and objects of the present invention having been completely described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. In a movable oshore drilling structure having a platform of generally rectangular shape with four corners, wherein at least four peripherally inwardly spaced columns depend from said platform, one of said columns `being located at each of said corners to provide opposing pairs of corner columns, the improvement which comprises auxiliary buoyancy means extending between the opposing pairs of said corner columns, said buoyancy means having a longitudinally extending side and a plurality of laterally extending slots for receiving said columns, said buoyancy means having a lateral dimension exclusive of said slots which is greater than the inward peripheral spacing of said columns, and means for locking said buoyancy means embracedly on said columns so that a portion of said buoyancy means extends outboard of said platform.

2. Apparatus in accordance with claim 1 wherein the buoyancy means are rectangular in shape and further include means for varying the buoyancy thereof.

3. An apparatus in accordance with claim 1 wherein the locking means include a plurality of locking pins having a free end retractable across said slots from contact with said columns so as to allow relative movement of said columns and said buoyancy means.

4. An apparatus in accordance with claim 3 wherein each of said locking pins includes an arcuate surface on the free end thereof adapted to contact the outer periphery of said column.

5. Apparatus for providing stability to a portable offshore drilling rig which has a rectangular bottom bearing member, a plurality of vertically extending columns connected to the bottom bearing member on their lower ends, and a rectangular platform supported by said columns on the upper ends of said columns, said platform having one column located at each corner thereof, which comprises vertically slidable auxiliary buoyancy means embracedly and removably arranged on the corner columns of said drilling rig with a portion of said buoyancy means extending inboard of said portable rig and the remaining portion extending outboard of said rig, said auxiliary buoyancy means being provided With a slot extending inwardly of said buoyancy means from one side thereof for flotationally placing on and removing said buoyancy means from said columns while maintaining said platform upon said columns, and means for securing said buoyancy means embracedly on said columns.

6. An apparatus in accordance with claim 5 wherein said securing means comprises a locking pin extending across the slot from one side thereof to the other, eX- terior of the position of said column when embracedly received therein.

References Cited in the file of this patent UNITED STATES PATENTS 672,356 Danisy-Martin Apr. 16, 1901 714,176 Hallett Nov. 25, 1902 2,900,794 Sutton Aug. 25, 1959 2,909,901 Suderow Oct. 27, 1959 2,938,354 Knapp May 31, 1960 2,944,403 Smith Iuly 12, 1960 FOREIGN PATENTS 612,201 Great Britain Nov. 9, 1948 

